Percussion tool incorporating a combustion cylinder for driving a reciprocable hammer piston



Aug. 22, 1967 B. v. NYHOLM 3,336,936

PERCUSSION TOOL INCORPORATING A COMBUSTION CYLINDER FOR DRIVING A RECIPROCAELE HAMMER PISTON Filed Feb. 24, 1965 4 Sheets-Sheet 1 Fig.

INVENTOR.

Bengt VIKtOR Ngholm Aug. 22, 1967 B. v. NYHOLM 3,336,936

PERCUSSION TOOL INCORPORATING A COMBUSTION CYLINDER FOR DRIVING A RECIPROCABLE HAMMER PISTON Filed Feb. 24, 1965 Fig. 2

INVENTOR.

Bengt VsKfoa' N helm geeefl, mama/1111 WFo/zmjy 4 Sheets-Sheet 2 Aug. 22, 1967 B. v. NYHOLM 3,336,986

PERCUSSION TOOL INCORPORATING A COMBUSTION CYLINDER FOR DRIVING A RECIPROCABLE HAMMER PISTON Filed Feb. 24, 1965 r 4 Sheets-Sheet 3 H 55 47 6 3. 40 W\ i I 50 I u 11 1| 45 Q1 l SR i I m m I 66 1- Fl' .5 58 cgjij- INVENTOR.

Bcflgi' Vi KioR. My helm Aug. 22 1967 a. v. NYHOLM 3,336,986

PERCUSSION TOOL- INCORPORATING A COMBUSTION CYLINDER FOR DRIVING A RECIPHOCABLE HAMMER PISTON Filed Feb. 24, 1965 4 Sheets-Sheet 4 I NVENTOR Bengt \MHUQ. hollnl BY gjqeek, mnacal flHoRNey United States Patent 3,336,986 PERCUSSION TOOL INCORPORATING A COM- BUSTION CYLINDER FOR DRIVING A RECIP- ROCABLE HAMMER PISTON Bengt Vilttor Nyholm, Naeka, Sweden,

Copco Aktiebolag, Nacka, Sweden Filed Feb. 24, 1965, Ser. No. 434,914 Claims priority, application Sweden, Mar. 6, 1964, 2,853/ 64 13 Claims. (Cl. 17373) This invention relates to percussion tools incorporating a combustion cylinder for driving a reciprocable hammer piston. In tools of this type a portion of the hammer piston is actuated by combustion gases in the combustion chamber for producing the percussion stroke and a counter pressure chamber actuates another portion of the hammer piston for producing the return stroke thereof. It has been customary to provide a pressure fluid source in the tool for feeding pressure fluid to the counter pressure chamber and to feed more pressure fluid thereto than actually necessary for maintaining a counter pressure level therein suflicient for proper reciprocation of the hammer piston. The excessive pressure fluid has been vented from the counter pressure chamber under the control of a needle valve and used for drill hole flushing purposes or passed to the atmosphere.

It is a primary object of the invention to provide an extended control of pressure fluid venting from the counter pressure chamber whereby the hammer piston can be set either to perform useful work or to pulsate idly simply by adjustment of the pressure level in the counter pressure chamber. Another object of the invention is to provide an efficient control of the secondary use of the pressure fluid vented from the counter pressure chamber. A still further object of the invention is to provide a simple combined means for attaining the above-mentioned two objects in combination with locking of the working implement against rotation and making of its rotation operative or inoperative at will.

In the accompanying drawings one embodiment of the invention is illustrated by way of example it being understood, however, that various modifications of the invention may be made within the scope of the claims.

FIG. 1 is a longitudinal sectional view through the tool coplanar with the crank shaft included therein, the tool being shown as provided with a differential trunk motor and compressor piston connected to the crank shaft and with a free opposed motion hammer piston. FIG. 2 is a longitudinal sectional view through the tool perpendicular to the crank shaft. FIG. 3 is a detail section of one end of the crank shaft and the means cooperating therewith for transmitting motion to a drill steel rotation mechanism. FIG. 4 illustrates on a larger scale a section on the line IV-IV in FIG. 1. FIG. 5 is a section on the line VV in FIG. 4. FIGS. 6 and 7 are cross sections on the respective lines VI-VI and VII-VII in FIG. 5. FIGS. '811 are fragmentary views illustrating different positions of the valve means included in FIG. 5. FIGS. 12-15 are fragmentary views corresponding to FIGS. 811 and illustrating the different positions of the ratchet means included in FIG. 4, which ratchet means is actuated by the valve means. FIG. 16 finally shows a section on the line XVI-XVI in FIG. 13.

The percussion tool illustrated in the drawings has a housing consisting of an assembly of a divided crank case 1, 2, a compressor cylinder 3, a motor cylinder 4, an auxiliary cylinder 5, and a lower casing 6. A crank shaft 7 is rotatably journalled in the crank case 1, 2 which is provided with two handles 8, 8. The crank case 1, 2 supports a fuel tank 9. The crank shaft 7 carries a flywheel assignor to Atlas Sweden, a corporation of surface said end face thus 10 provided with a rope starter drum 11 for starting of the tool, a magneto 12 for generating ignition current, and a cooling fan 13 operating in a spiral casing 14 formed in the crank case portion 2. A connecting rod 15 is journalled on the crank pin of the crank shaft 7 and connected by means of a piston pin 16 to the differential trunk motor and compressor piston. Said piston consists of a motor portion 17, a sleeve portion 18 and a compressor portion 19. The motor portion 17 in conventional manner controls openings in the motor cylinder 4 through which scavenging air and fuel is supplied to the combustion chamber 29 of the motor cylinder through passages 20 leading to the combustion chamber from the crank case. Scaven-ging air is drawn into the crank case and compressed therein by the differential motor and compressor piston 17, 19. Fuel is supplied to the scavenging air from the tank 9 via a carburetor, not illustrated in the drawings. 21 indicates a spark plug and 22 an exhaust manifold. 23 is a sealing ring provided between the combustion chamber 29 and the compressor cylinder chamber 25 and forming a seal with the sleeve portion 18 of the differential piston 1719.

The compressor piston portion 19 draws air through an opening controlled by a valve 24 into the annular compress-or cylinder chamber 25 and compresses the air therein and delivers it over a valve 26 through a conduit 27 to a counter pressure chamber 28 in the lower casing 6 which chamber forms a pressure fluid reservoir. A free opposed motion hammer piston is reciprocable in the combustion chamber 29, the upper and lower cylinder chambers 37, 39 of the auxiliary cylinder 5 which have a larger diameter than the motor cylinder chamber 4, and in a through bore 31 in a guiding portion 32 forming a partition between the lower auxiliary cylinder chamber 39 and a flushing chamber 40 formed in the lower casing 6 below the auxiliary chamber 39. The hammer piston consists of a motor portion 33 which fits into the combustion cylinder chamber 29 and is provided with piston rings, an intermediate portion 34 with large diameter which is movable in the auxiliary cylinder 5 dividing it into the upper and lower auxiliary piston chambers 37 and 39, and a cylindrical stem 35 for delivering impacts and sliding in the through bore 31 of the guiding portion 32 with a tight fit, whereby leakage of pressure fluid from the lower auxiliary chamber 39 to the flushing chamber 40 gss prevented during reciprocation of the hammer piston Compressed air, which is compressed in the compressor cylinder chamber 25 by the compressor piston portion 19, flows from the counter pressure chamber 28 through radial openings 36 to the upper auxiliary cylinder chamber 37 at the upper side of the intermediate piston portion 34, and through radial openings 38 into the lower auxiliary cylinder chamber 39 between the intermediate piston portion 34 and the guiding portion 32. The pressure fluid cushion in the auxiliary chamber 37 prevents the hammer piston from hitting against the upper end face of chamber 37 by means of the upper face of the intermediate piston portion 34 while the pressure fluid in the lower auxiliary chamber 39 is responsible for providing the return stroke of the hammer piston 33-35.

In the tool shown a drill steel chuck 41 is rotatably journalled in the lower casings 6 and extends into the flushing chamber 40. A drill steel retainer 42 is pivotally journalled on the lower casing 6, FIG. 2,. and serves to retain the preferably hexagonal neck 48 of a drill steel 43 or some other working implement within the drill steel chuck 41 during work. The upper end surface of the drill chuck 41 abuts slidably against the lower end face of the guiding portion 32. By offering a large axial bearing provides a thrust bearing for the transmission of feeding pressure from the percussion tool to the drill steel chuck and to the working implement therein. The flushing chamber 40 communicates through radial passages 47 in the guiding portion 32 with a chamber adjacent the upper end of the implement neck 48. In the case of a drill steel 43 there is usually provided a flushing passage 44 axially therethrough which thus will receive pressure fluid from the flushing chamber 40 except for the short instants when the hammer piston stem delivers its impacts. A packing 49 between the neck 48 and the drill chuck 41 prevents flushing fluid from leaking along the neck 48 to the surrounding atmosphere.

For enabling turning of the drill steel 43 the drill chuck 41 is formed integral with a ratchet wheel 50 having teeth for cooperation with a pawl 51 which is arranged to rotate the wheel 50 stepwise in a certain direction. To this end the locking pawl 51 is hinged on an arm 52 fixedly connected to an axle 53 which performs an oscillating turning motion during operation of the percussion tool. A spring 54 keeps the pawl 51 normally in engagement with the ratchet wheel 50. The oscillating turning motion of the axle 53 is taken out from the crank shaft 7 for which purpose one end thereof has a slanting pin 55 thereon, FIGS. 1, 3, set at an angle with respect to the axis of rotation of the crank shaft 7. A block 56 is slidable and rotatable on the pin 55 and the block is also slidable non-rotatably in the forked end 57 of the oscillatable turning axle 53. When the crank shaft 7 turns one revolution this well known motion transmission device forces the axle 53 and the arm 52 thereon to produce an oscillating turning movement, which causes the locking pawl 51 to oscillate and to turn the ratchet wheel 50 together with the drill chuck 41 and the drill steel 43 nonrotatably received therein. A catch 45 pivotally mounted in the lower casing 6 is biased by a spring 46 against the ratchet wheel 50 and prevents the latter from rotating in the return direction of the locking pawl 51.

In the lower casing 6 there is rotatably journalled a spindle 58 tightly extending from the outside through a bore 62 into the flushing chamber 40. The spindle 58 is a combined rotary valve plug for controlling the pressure level in the counter pressure chamber 28, an uncoupling device for the pawl 51 and an arresting device for the drill chuck 41. The spindle 58 is provided with a handle 59 accessible from the outside of the lower casing 6 so that the spindle 58 can be turned easily. A spring pressed detent 60 cooperates with a number of alternative notches 61 on the spindle 58 for retaining the latter in different positions of angular adjustment. The notches are arranged in the bottom surface of a groove 63 receiving the detent 60 whereby the spindle 58 is retained axially in the bore 62. The inner portion of the spindle 58 disposed in the flushing chamber is finger-shaped and positioned adjacent to the periphery of the ratchet wheel 50. A lug 64 disposed at an angle to the axis of the spindle 58 forms a finger tip thereon and in the position shown in FIG. 4 the lug 64 lies freely between the ratchet wheel 50 and the pawl 51 allowing the latter to oscillate in order to rotate the ratchet wheel 55. A locking tooth 68 on the spindle 58 which in certain positions thereof can arrest the ratchet wheel 50 against rotation, takes an inactive position as illustrated in FIG. 4 at the side of the spindle 58 opposite to the ratchet wheel 50. In the bore 62 the spindle 58 forms a valve plug for controlling an outlet or venting passage 65 from the counter pressure chamber 28. In the position depicted in FIGS. 4 and 5 the spindle 58 presents a bore 67 and a restricted aperture 66 to the passage 65 thus connecting the counter pressure chamber 28 to the flushing chamber 40.

When the spindle 58 by means of the handle 59 is turned counter-clockwise 90 (seen in FIG. 7) from the above described position to the position in FIGS. 8 and 12, the slanting lug 64 engages the pawl 51 turning it aside so that its engagement with the ratchet wheel 50 is interrupted and the ratchet means provided by the pawl 51 and wheel 50 is made inoperative to rotate the drill chuck 41. In the new position the tooth 68 still occupies inactive position outside of the ratchet wheel 50 while the spindle 58 presents a wide venting groove 69 to the passage 65 connecting the counter pressure chamber 28 to the flushing chamber 40.

Continued turning of the spindle 58 in the counterclockwise direction can be performed only upon manual depression of a spring pressed catch 70, FIG. 4, lying in the way of the handle 59, whereupon the spindle 58 can be turned to the position depicted in FIGS. 9 and 13. In this position the spindle 58 presents a central bore 71 which leads axially outwardly to the atmosphere, and a large radial venting bore '72 to the passage 65 whereby the counter pressure chamber 28 is vented to the atmosphere. The tooth 68 now engages one of the teeth on the ratchet wheel 50, FIG. 16, arresting rotation of the latter and the lugs 64 still keeps the ratchet means 50, 51 inoperative.

As a result of further counterclockwise turning of the spindle 58 to the position depicted in FIGS. 10 and 14, there is presented to the passage 65 a radial bore 74 having a restricted aperture 73 therein and communicating with the central bore 71 in the spindle 58. The tooth 68 still arrests the ratchet wheel 50 and the lug 64 keeps the ratchet means 50, 51 inoperative.

If desired a still further angular position of adjustment of the spindle 58 can be provided for example upon turning of the spindle 58 from the position depicted in FIGS. 10, 14 to the position depicted in FIGS. 11 and 15. In this latter position the detent 60 prevents further counter-clockwise turning of the handle 59 by locking against a stop screw 75 screwed into the bottom portion of the groove 63. In this extreme position the passage 65 is shut off entirely by the spindle 58, the ratchet wheel 50 remaining arrested by the tooth 68 and the ratchet means 50, 51 are made inoperative by the lug 64. There is now created a maximum pressure level in the counter pressure chamber 28 and one can conveniently take out pressure fluid from the chamber 28 for external use via a valve nipple 76, FIG. 5, and a hose (not shown) connected thereto.

When the percussion tool shall be operated as a rock drill and started, the handle 59 is firstly turned counter clockwise from the position shown in FIGS. 4-7, the spindle 58 thus taking up the position shown in FIGS 8, 12. This causes the lug 64 to move the pawl into inoperative position so that no turning of the drill chuck 41 can take place when the crank shaft 7 starts to rotate. By the aid of a starting rope, not shown, the rope starter drum 11 is rotated so that the motor portion of the tool starts operating while runing idle. Compressed air, which is generated by the compressor piston portion 19 in the chamber 25 and which through the conduit 27 is delivered to the counter pressure chamber 28, passes through the venting passage 65 and the groove 69 in the spindle 58 to the flushing chamber 40 and then-cc to the flushing passage 44 for blowing the drill steel 43 clean. The groove 69 is of such width that the pressure level in the counter pressure chamber 28 and in the cylinder chamber 39 will be low and will only be enough for causing some pulsating movement of the hammer piston 33-35 substantially without impact power. During idle running and drill hole blowing the hammer piston thus does not produce useful impact work.

For drilling the handle 59 is turned 90 in clockwise direction back to the position depicted in FIGS. 4-7 whereby the ratchet means 51, 50 again is made operative by the lug 64 to rotate the drill chuck 41 and steel 43. The flushing air vented via the passage 65 now passes the restricted aperture 66 in the spindle 58 whereby the pressure level in the counter pressure chamber 28 and in the lower auxiliary cylinder chamber 39 rises so that the hammer piston 33-35 is lifted and starts to reciprocate and to deliver impacts as defined by fluid compression and gas expansion in the combusion chamber 29 adjacent the motor piston 17. Flushing by pressure fluid takes place via the restricted aperture 66, the bore 67 the flushing chamber 40, and the drill steel 43.

If it is desired to use the percussion tool as a breaker or as a spade or the like, in which case rotation of the implement is undesirable, the drill steel 43 is exchanged for a chisel, spade or other working implement and its preferably hexagonal neck portion is inserted into the drill chuck 41. The tool is started upon angular setting of the handle 59 counter-clockwise past the security catch 70 in the depressed position of the latter whereby the spindle 58 is turned to the position shown in FIGS. 9, 13. Starting thus results in idle runing of the tool hammer piston 33-35 pulsating without performing useful impact work since venting of pressure fiuid via the large bores 72, 71 directly to the atmosphere will keep the pressure level in the counter pressure chamber too low to produce the return stroke of the hammer piston 3345. Simultaneously the tooth 68 arrests rotation of the ratchet wheel 50 and the drill chuck 41 while the lug 64 keeps the pawl 51 in the ratchet means 50, 51 inoperative to rotate the drill chuck 41.

When the chisel or spade is ready for work the handle 59 is turned further in counter-clockwise direction until the spindle 58 occupies the position shown in FIGS. 10, 14. The restricted aperture 73 in the venting passages 74, 73, 71 to the atmosphere causes an increase of the pressure level in the counter pressure chamber 28 so that the hammer piston 33-35 starts to reciprocate and to deliver impacts with full impact power against the neck of the working implement. Simultaneously the drill chuck 41 is locked by the tooth 68 and the ratchet means 50, 51 is made inoperative by the lug 64.

In the position shown in FIGS. 11, there is produced a maximum pressure level in the counter pressure chainber 28 and when pressure fluid is taken out for external use through the nipple 76 the percussion tool for example can be laid on the ground with the drill chuck 41 empty. During its reciprocations the hammer piston 33-35 will be caught by the opposed pressure cushions trapped in the auxiliary cylinder chambers 37, 39 by the large diameter piston portion 34, which prevents the tool from receiving harmful blows.

The percussion tool described above and shOWn in the drawings naturally only is to be considered as an example and can be modified in its details in many different ways within the scope of the claims. The invention for eX- ample can be applied in internal combustion motor driven percussion tools in which rotation can be provided in other Ways than shown and the invention furthermore can be used in connection with percussion tools in which combustion gas under pressure is used for flushing and for return of the hammer piston instead of compressed air, with the gas being taken out from a suitable portion of the combustion chamber. The invention can also be applied in connection with percussion tools in which a special piston separate from the motor piston is arranged for generating the compressed air which is needed respectively for operation of the tool and for flushing of the drill steel.

What I claim is:

1. In a percussion tool, a combustion cylinder forming part of said tool, a hammer piston in said tool reciprocable to perform a percussion stroke and a return stroke with respect to said combustion cylinder, a portion of said hammer piston being actuated by combustion gases in said combustion cylinder to produce the percussion stroke thereof, a counter pressure chamber formed in said tool for actuating another portion of said hammer piston to produce the return stroke thereof, a pressure fluid source in said tool, means for feeding pressure fluid from said source to said counter pressure chamber, and a manually operable valve member communicating with said counter pressure chamber, said valve member having a working position presenting to said counter pressure chamber a restricted venting passage for maintaining a pressure level in said counter pressure chamber sufficient to produce reciprocation of said hammer piston with full impact power, said valve member also having an idle position presenting to said counter pressure chamber a large venting passage of such width that reciprocation of the hammer piston due to a decrease of the pressure level in the counter pressure chamber is replaced by a pulsating movement substantially without impact power.

2. A percussion tool as set forth in claim 1 in which a drill steel chuck is mounted in said tool, a hollow drill steel in said drill chuck and actuated. by said hammer piston, and a flushing chamber in said tool in communication with said chuck and drill steel, said valve member being provided with first and second large venting passages and presenting in a first idle position thereof said first large venting passage to said counter pressure chamber for directing pressure fluid therefrom to said flushing chamber to blow said drill steel, and said valve member in a second idle position thereof presenting said second large venting passage to said counter pressure chamber for directing pressure fluid therefrom to the atmosphere.

3. A percussion tool as set forth in claim 1 in which a drill steel chuck is rotatably mounted in said tool, a hollow drill steel in said drill chuck and actuated by said hammer piston, and a flushing chamber in said tool in communication with said chuck and drill steel, said valve member being provided with first and second restricted venting passages and presenting in a first working position thereof said first restricted passage to said counter pressure chamber for directing pressure fluid therefrom to said flushing chamber to blow said drill steel, and said valve member in a second working position thereof presenting said second restricted passage to said counter pressure chamber for directing pressure fluid therefrom to the atmosphere.

4. A percussion tool as set forth in claim 2 in which there is provided a manually releaseable catch in said tool between said first and second idle positions of said valve and operable to prevent said valve member from being moved directly from said first idle position to said second idle position and vice versa.

5. A percussion tool as set forth in claim 1 in which said valve member is provided with a shut off position for interrupting the venting therethrough for purposes of establishing a maximum pressure level in. said counter pressure chamber, said counter pressure chamber being provided with a connection allowing pressure fluid to be taken out for external use.

6. A percussion tool as set forth in claim 3 in which there are provided ratchet means in said tool for the rotation of said drill chuck, and power means in said tool independent of said hammer piston for driving said ratchet means, said valve member having first and second abutment means thereon operable in said second Working position of said valve member respectively to make said ratchet means inoperative to rotate said drill chuck and to positively lock said drill chuck against rotation.

7. In a percussion tool, a combustion cylinder forming part of said tool, a hammer piston in said housing reciprocable to perform a percussion stroke and a return stroke with respect to said combustion cylinder, a portion of said hammer piston being actuated by combustion gases in said combustion cylinder to produce the percussion stroke thereof, a counter pressure chamber formed in said tool for actuating another portion of said hammer piston to produce the return stroke thereof, a pressure fluid source in said tool, means for feeding pressure fluid from said source to said counter pressure chamber, a passage connected to said counter pressure chamber for diverting pressure fluid therefrom, a drill steel chuck rotatably mounted in said tool, a hollow drill steel in said drill chuck and actuated by said hammer piston, a flushing chamber in said tool in communication with said chuck and drill steel, and a valve member connected to said diverting passage, said valve member being provided with first and second restricted valve passages and presenting in a first working position whereof said first restricted passage to said diverting passage for directing pressure fluid from said counter pressure chamber to said flushing chamber to blow said drill steel, and said valve member in a second working position thereof presenting said second restricted valve passage to said diverting passage for directing pressure fluid from said counter pressure chamber to the atmosphere, said restricted valve passages in both said working positions maintaining such a pressure level in said counter pressure chamber that reciprocation of said hammer piston is provided with full impact power.

3. A percussion tool as set forth in claim 7 in which said valve member has an idle position intermediate said working positions and presenting to said diverting passage a large valve passage of such width that the reciprocation of the hammer piston due a decrease of the pressure level in the counter pressure chamber is replaced by a pulsating movement substantially without impact power.

9. In a percussion tool a combustion cylinder forming part of said tool, a hammer piston in said housing reciprocable to perform a percussion stroke and a return stroke with respect to said combustion cylinder, a portion of said hammer piston being actuated by combustion gases in said combustion cylinder to produce the percussion stroke thereof, a counter pressure chamber formed in said tool for actuating another portion of said hammer piston to produce the return stroke thereof, a pressure fluid source in said tool, means for feeding pressure fluid from said source to said counter pressure chamber, a drill steel chuck rotatably mounted in said tool, a hollow drill steel in said drill chuck and actuated by said hammer piston, a flushing chamber in said tool in communication with said chuck and drill steel, and adjustable valve member communicating with said counter pressure chamber for con trolling venting of pressure fluid therefrom and thereby of the pressure level in said counter pressure chamber, said valve member having alternative valve passages therein for directing pressure fluid from the portion of said counter pressure chamber in permanent communication with said feeding means at will either to said flushing chamber to blow said drill steel or to the atmosphere depending on the position of adjustment of said valve member.

10. In a percussion tool, a combustion cylinder forming part of said tool, a hammer piston in said housing reciprocable to perform a percussion stroke and a return stroke with respect to said combustion cylinder, a portion of said hammer piston being actuated by combustion gases in said combustion cylinder to produce the percussion stroke thereof, a counter pressure chamber formed in said tool for controlling the pressure fluid for actuating another portion of said hammer piston to produce the return stroke thereof, a pressure fluid source in said tool, means for feeding pressure fluid from said source to said counter pressure chamber, a drill steel chuck rotatably mounted in said tool, a drill steel in said drill chuck and actuated by said hammer piston, a ratchet wheel disposed in said tool for the rotation of said drill chuck, power means in said tool for driving said ratchet wheel, a spindle rotatably mounted in said tool adjacent said drill chuck, a manually operable handle connected to said spindle for the actuation thereof, and abutment means disposed on said spindle for the direct engagement of one of the teeth of said ratchet wheel within a certain angle of turn of said spindle to make said ratchet wheel inoperative to rotate said drill chuck while simultaneously positively locking said drill chuck against rotation.

11. A percussion tool as set forth in claim 10 in which there are provided passage means in said spindle operable to connect within said certain angle of turn of said spindle said counter pressure chamber to the atmosphere.

12. In a percussion tool, a combustion cylinder forming part of said tool, a hammer piston in said housing reciprocable to perform a percussion stroke and a return stroke with respect to said combustion cylinder, a portion of said hammer piston being actuated by combustion gases in said combustion cylinder to produce the percussion stroke thereof, a counter-pressure chamber formed in said tool for actuating another portion of said hammer piston to produce the return stroke thereof, a pressure fluid source in said tool, means for feeding pressure fluid from said source to said counter-pressure chamber, a drill steel chuck rotatably mounted in said tool, a drill steel in said drill chuck and actuated by said hammer piston, ratchet means in said tool for the rotation of said drill chuck, power means in said tool for driving said ratchet means, a spindle rotatably mounted in said tool adjacent said drill chuck, a manually operable handle connected to turn said spindle upon actuation thereof, abutment means on said spindle operable within a certain angle of turn thereof to make said ratchet means inoperative to rotate said drill chuck and simultaneously to positively lock said drill chuck against rotation, and venting passages in said spindle of different width therein connectable to said counter-pressure chamber for changing the pressure level therein in dependence upon the position of turn of said spindle.

13. A percussion tool as set forth in claim 12 in which two alternative venting passages of different width are connectable with said counter pressure chamber within said certain angle of turn of said spindle.

References Cited UNITED STATES PATENTS 1,389,539 8/1921 Turner l7373 X 1,709,024 4/1929 Katterjohn 17373 X 1,902,562 3/1933 Lear 17373 X 2,764,138 9/1956 Wahlsten et al. 173-122 X 3,231,028 1/1966 Alcock et al 173-76 FRED C. MATTERN, ]R., Primary Examiner.

HALL C. COE, Assistant Examiner. 

1. IN A PERCUSSION TOOL, A COMBUSTION CYLINDER FORMING PART OF SAID TOOL, A HAMMER PISTON IN SAID TOOL RECIPROCABLE TO PERFORM A PERCUSSION STROKE AND A RETURN STROKE WITH RESPECT TO SAID COMBUSTION CYLINDER, A PORTION OF SAID HAMMER PISTON BEING ACTUATED BY COMBUSTION GASES IN SAID COMBUSTION CYLINDER TO PRODUCE THE PERCUSSION STROKE THEREOF, A COUNTER PRESSURE CHAMBER FORMED IN SAID TOOL FOR ACTUATING ANOTHER PORTION OF SAID HAMMER PISTON TO PRODUCE THE RETURN STROKE THEREOF, A PRESSURE FLUID SOURCE IN SAID TOOL, MEANS FOR FEEDING PRESSURE FLUID FROM SAID SOURCE TO SAID COUNTER PRESSURE CHAMBER, AND A MANUALLY OPERABLE VALVE MEMBER COMMUNICATING WITH SAID COUNTER PRESSURE CHAMBER, SAID VALVE MEMBER HAVING A WORKING POSITION PRESENTING TO SAID COUNTER PRESSURE CHAMBER A RESTRICTED VENTING PASSAGE FOR MAINTAINING A PRESSURE LEVEL IN SAID COUNTER PRESSURE CHAMBER SUFFICIENT TO PRODUCE RECIPROCATION OF SAID HAMMER PISTON WITH FULL IMPACT POWER, SAID VALVE MEMBER ALSO HAVING AN IDLE POSITION PRESENTING TO SAID COUNTER PRESSURE CHAMBER A LARGE VENTING PASSAGE OF SUCH WIDTH THAT RECIPROCATION OF THE HAMMER PISTON DUE TO A DECREASE OF THE PRESSURE LEVEL IN THE COUNTER PRESSURE CHAMBER IS REPLACED BY A PULSATING MOVEMENT SUBSTANTIALLY WITHOUT IMPACT POWER. 